BigAppleBucky:
I don’t know why folks are discussing a Democratic majority in the House. It just will not happen. Sure, the Democratic House candidates will probably garner five or even ten million more votes nationwide, the the GOP will only lose a few seats.
Gerrymandering works by giving the controlling party slim majorities in many districts and concentrating opposition voters in a few districts. So if everyone votes the way they have in the past, the controlling party gets a disproportionate number of seats. But, if those slim majorities slip away, you get a tidal wave going the other direction.
I worked out the math for the case of Ohio:
I think many people underestimate the potential impact of gerrymandering. Take Ohio, for example. The voting indices by district, in order from pro-Republican (+) to pro-Democrat (-) are: +14, +9, +9, +8, +8, +6, +6, +5, +5, +5, +3, +2, -12, -14, -15, -30 . The baseline is 12 R and 4 D in the House, if the presidential race has no down-ticket impact. If there’s a 3.5-point effect in favor of the Democrats, it’ll go 10 R, 6 D. A 5.5-point effect, results in 7 R, 9 D. And 6.5 goes to 5 R, 11 D. In contrast, even a 10-point shift in favor of the Republicans does not result in the Democrats losing any seats.
Gerrymandering really tilts the results non-linearly.
Of course, what are the odds of a 5 or 6 point shift in favor of the Democrats? I’m not sure, but when something like 30% of the Republicans are not happy with their nominee, it wouldn’t take “something extraordinary”. More like “against the odds, but possible”. I’ll be very interested in Nate Silver’s analyses.